Latin hymn to God the Father and Christ the Son, traditionally sung
on occasions of public rejoicing (coronation of kings, proclamation of
bishops, consecration of a virgin, canonization of a saint, divulgation
of a peace treaty or a victory).

According to legend, it was improvised antiphonally by St.
Ambrose and St. Augustine at the
latter's baptism. It has more plausibly been attributed to Nicetas,
bishop of Remesiana in the early 5th century, and its present form--equal
sections devoted to the Father and Son, a half-clause to the Holy Spirit,
followed by a litany--fit in historically with part of the Arian controversy
(over the nature of Christ) of the 4th century. Much of the text is composed
of traditional statements of belief; and unlike most hymns, it is prose.
The melody derives from various pre-Gregorian and Gregorian melodic styles.
It has been set polyphonically by the British composers Henry Purcell,
Ralph Vaughan Williams, and Benjamin Britten, as well as by George Frideric
Handel, Hector Berlioz, Zoltán Kodály, Anton Bruckner, and
Antonín Dvorák.